Well known in the art are video security systems that present an observer located at a video monitoring facility with a succession of images of different areas, each area being viewed by a lens of a different video camera. However, these video systems are completely passive in the sense that detecting an intrusion into the area viewed by the camera's lens remains the responsibility of the observer. That is, the video camera provides the observer with no assistance in detecting an intrusion. Thus, if the observer at the video monitoring facility is distracted or fails to notice the occurrence of an intrusion, no alarm will be raised. It is also possible that the occurrence of an intrusion might be missed because images of other areas are being presented to the observer at the instant the intrusion occurs. Furthermore, because the video signal from each video camera must be transmitted to the video monitoring facility by a wide bandwidth, coaxial cable, or by some other type of wide bandwidth, dedicated communication channel such as a microwave link, it is commercially impractical to distribute this type of video security system at sites randomly located within an extended geographic area, such as throughout a large city.
In addition to well known, passive security systems of the type described above, active, motion sensing video systems have been developed for military battlefield applications. However, these experimental military systems were physically very large, e.g. were carried on a trailer and towed by a jeep, consumed hundreds of watts of power, and were very expensive.
Recently, throughout the world, telephone systems have begun providing digital communication capability in accordance with the Integrated Services Digital Network ("ISDN") standard established by the International Telegraph and Telephone Consultative Committee ("CCITT"). Under this CCITT standard, a basic ISDN access consists of two full-duplex 64 kilobits per second ("kbps") digital data channels, called channel B1 and channel B2, plus another full-duplex 16-kbps digital channel, called a D channel. Under the CCITT standard, using time division multiplexing, all three of these digital data channels may be transmitted over a single pair of twisted wires, or over two pairs of twisted wires. While ISDN basic access was originally intended to provide voice and slow speed data communication services, over the years developments in digital signal processing and compression techniques have advanced technology to the extent that compressed video data may now be transmitted using an ISDN basic access communication channel. These techniques have progressed to such an extent that there now exist several alternative video data compression techniques such as the CCITT H.261 picture phone standard, the Joint Photographic Experts Group ("JPEG") standard, and the Moving Picture Experts Group ("MPEG") standard that permit transmission of video images over an ISDN basic access communication channel. Furthermore, the CCITT has established a standard H.221 which permits intermixed transmission over an ISDN basic access communication channel of images compressed in accordance with both the H.261 picture phone standard, and images compressed in accordance with the JPEG standard.